Felted article and process for its production



Patented June 9, 1942 FELTED ARTICLE AND'PROCESS FOR ITS PRODUCTION Aubrey E. Broderick, South Charleston, WV. assign'or to Carbide and Carbon Chemicals poration, a corporation of New York No Drawing. Application March 21, 1941, Serial No. 384,480

19 Claims.

a This invention relates to the production of fibrous sheets and continuous webs of cellulosic fibrous materials; and more especially it concerns the production, from unrefined or more or less refined cellulose fibers, such as wood pulps, of soft, water absorbent fabrics of unwoven fibers,

which fabrics possess high wet and dry strengths,

substantial wet stretch, a high degree of moisture absorption, permeability to air, and a high resistance to linting. The novel products of the invention are especially adapted for use in the manufacture of paper toweling .and a wide variety of other kinds of liquid absorbent tissue and sheeting in wide use today for cleaning purposes, and for wrapping or otherwise protecting articles.

Numerous attempts have been made heretofore by manufacturers of paper toweling, absorbent tissue and the like, to improve the wet strength of such materials and to prevent the linting thereof. Ordinary cellulosic fibers, such as wood pulp, when felted into a thin sheet, to form a soft absorbent paper, provide a sheet having little strength when wet with water. Such a sheet may be coated with a sizing material or a varnish to increase the wet strength. However the water absorption of the sheet is thereby decreased, since the varnishes-and the like used for the purpose generally are water repellent.

Other attemptsto increase the wet strength and the resistance to linting of paper toweling have involved the impregnation of special high grades of long-fiber sulfite wood pulp with a viscose solution, the treated product being run through a precipitating bath, followed by the usual desulfurization, bleaching and washing operations. The resultant product, while satisfactory for the intended purpose, is relatively expensive, in view of the involved operations required for its production.

Among the more important objects of this invention are: The production in novel manner of absorbent sheets or continuous webs of unwoven fibrous cellulosic material having high wet and dry strengths under service conditions; and to provide a novel article, such as a sheet of paper toweling or absorbent paper tissue, which is highly resistant to linting; has a high rate of moisture absorption; may be rendered sufiiciently pervious to air that it can breathe; and can stretch somewhat in the wet condition Without coating of the cellulosic fibers with an acetal of the type hereinafter described.

In accordance with the invention, either unrefined or refined cellulosic fibers, or continuous webs or discontinuous sheets or other shaped articles comprising these fibers, such as paper toweling and absorbent tissues of the types produced by known commercial processes, are more or less uniformly impregnated or at least some of the fibers thereof treated with a solution adapted, upon drying or heating of the treated article, to form an acetal derivative of an ether of one of the higher polyoses in intimate contact with fibers of the cellulosic sheet or web.

, Wood fibers are especially suitable as the cellulosic fibrous material, because of their cheapness and availability. Long-fibered pulp may be made from spruce, tamarack or jack pine, preferably by the well known sulfate process or the sulfite process for making wood pulp. Wood fibers admixed with some cotton fibers or linen fibers provide a sheet having increased strength. The fibers may be bleached or otherwise refined prior to use. water to obtain the necessary felting properties, may be mercerized to a limited extent, if desired,

, to increase their absorptive capacity.

The aforesaid impregnating or coating solution may be made by dissolving in an aqueous liquid, conveniently at or around room temperature with agitation, a water-soluble cellulose ether containing at least some free hydroxyl groups, such as a water-soluble hydroxyethyl cellulose, or a watersoluble partially alkylated cellulose, such as methyl or ethyl cellulose. There is then dissolved in the aqueous liquid, a water-soluble aldehyde having the structure designated by the formula -method disclosed on page 8 and in Example IV of United States Patent No. 1,941,278 of A. W. Schorger. Likewise water-soluble partially alkylated celluloses, such as a medium viscosity watersoluble methyl cellulose,'are effectively used in the process. The last-named ethers evidently contain from one to two methyl groups for each glucose anhydride unit.

It is preferred to use in the process, dialyzed aqueous solutions of the cellulose ethers. However, undialyzed solutions may be used, and provide products suitable for certain purposes; Al-

though "catalysts for the acetal-type condensation The fibers, after being beaten in" reaction, such as mineral acids, may be present in the solution of cellulose ether, the use of catalysts is in general objectionable, due to practical difiiculties encountered in the removal of the catalysts and their reaction products from the final product. The acetal-type reaction goes to virtual completion as the water is removed, even in the absence of a catalyst.

Preferably, in order to provide a final product which not only has greatly improved wet strength and dry strength and resistance to linting but also possesses the properties of flexibility and pliability or a soft hand to a highly satisfactory degree, one or more polyhydric alcohols, such as ethylene and diethylene glycols, the propylene glycols, and glycerol, may be added to the aqueous solution of cellulose ether and glyoxal or equivalent aldehyde. Thereby, upon drying the fibrous cellulosic material, or the web or sheet formed therefrom; which has been treated with such solution, the fibers forming the sheet are coated with a product that is formed by the concurrent condensation,apparently a form of conjoint acetalization,-of the watersoluble cellulose ether and of the polyhydric alcohol with the aforesaid aldehyde. Paper toweling and thin sheets of cellulosic tissue impregnated with such product have greatly improved wet and dry strengths, and are resistant to linting, while at the same time having improved resistance to tear when wet, and a satisfactory tensile strength.

To make a product suitable for use as towels or absorbent tissue, the cellulosic fibers may be treated with the aqueous solution in the pulp heaters. It is preferred however to apply the solution to the felted sheet. This may be accomplished in any of a number of ways, as by the use of "doctor rolls. or by spraying or brushing the solution upon the sheet either uniformly or in selected zones, to form either continuous or discontinuous films of the solution on the fibers; or by passing the sheet or web through a bath containing the treating solution.

The drying of the treated web or article may be conducted conveniently at temperatures around 100 0., although higher and lower temperatures are quite satisfactory for the purpose. The drying step facilitates the condensation reaction between the cellulose ether and the aldehyde,-or between the cellulose ether, polyhydric alcohol and a1dehyde,present in the composition with which the cellulosic fibers are surfaced or impregnated.

The following example will illustrate one form of the invention:

A commercially available type of unbleached paper toweling. produced from sulfate wood pulp and weighing about 0.28-0.29 pound per square yard, was conditioned at 35% relative humidity and 77 F. Samples of the toweling were impregnated with a solution prepared by mixing together the following ingredients:

Parts by weight Water-soluble hydroxyethyl cellulose 4.85 Glycerine 4.85 Glyoxal 1.94 Water 988.5

The samples were impregnated with this mixture by brief immersion in the approximately 1% solution. Excess solution was removed from the towel by passing the latter through pressure rolls. The towel was then dried at a temperature between 90 and 100 C. during approximately two soda, after which it was shredded and stored at.

a temperature within the range from 20 to 30 C. for 168 hours. The aged alkali cellulose was reacted for about eight hours in a baratte with ethylene oxide vapors in amount approximately of the dry weight of the cellulose, at room temperature and under a pressure near but below atmospheric pressure, in the absence of air. The resultant mass was dissolved in water, and the caustic soda was neutralized with acetic acid (other acids may be used). The sodium salts thus formed were removed by dialysis. (Other known methods may be used for isolating and removing the inorganic salts.) A seamless tube of regenerated cellulose was filled with the crude water-soluble hydroxyethyl cellulose, and was bathed in warm running water until the ash content of the crude product was reduced to approximately 1% or less, based on the weight of total solids in the solution.

In preparing the treating solution the glyoxal was added to the aqueous solution of dialyzed water-soluble hydroxyethyl cellulose, glycerine and water; and the mixture was stirred at room temperature until solution of the glyoxal was effected. The impregnation of the cellulosic material resulted in an average increase of around 1.36% of the original dry weight of the untreated fiber. The treated paper toweling had an average increase in dry bursting strength of 23% over the strength of the untreated paper; and had an average increase in wet bursting strength of 162% over the strength of the untreated paper.

In instances where the paper was subjected to two successive impregnation and. drying steps, the total increase in weight due to the impregnatin material averaged 1.82%; showed an increase in dry bursting strength averaging 39% above that possessed by the untreated paper; and an increase in wet bursting strength of over 300% of that of the untreated paper. In instances involving a triple impregnation with the aforesaid solution, and interspersed with drying steps, there was an average increase in weight of 3.74% due to impregnating material. At the same time the dry bursting strength increased an average of 54%; and the wet bursting strength increased on an average of 450% over that of the untreated paper.

In making the test for wet strength, each towel was 'immersed in water at 50? C. for 30 seconds. The moisture absorptioncapacity tends to fall of! as the percentage of the impregnating material increases. Nevertheless, in instances where such material is around 1.5% or less of the dry weight of the cellulose material, the absorbency is fullyas good as that of the untreated material.

Even extremely high grade paper towels having high wet strength, such as those made from selected long fibers of unbleached or bleached spruce sulfite wood pulp, may be improved by the treatment of this invention. Indeed, towels made from a high grade of sulfite wool pulp and which had been impregnated with a viscose solution,

while the product 7 2,285,490 the viscose precipitated thereon, purified, and the toweling bleached, was impregnated with the solution mentioned in the example in the manner therein indicated. A single impregnation, followed by a drying treatment in the manner indicated, yielded a product that had increased in weight 1.34% over the dry weight of the towelingfwhile the wet strength'thereof had increased 20% of the wet strength of the untreated toweling. Samples of this high strength toweling which had received two successive impregnations increased in weight an average of 2.7%. At the same time the dry strength of the toweling increased by around 24%; and the wet strength thereof increased around 126% of the strength of the untreated toweling.

Water-soluble alkyl celluloses may be substituted for the hydroxyetlrvl cellulose mentioned. Upon treating the unbleached toweling recited in the example with a solution prepared by mixing a medium viscosity water-soluble methyl cellulose (a 2% aqueous solution of which has a viscosity of about 50 centipoises at 20 0.), glyoxal, glycerine and water in the general proportions named in the example, substantially the same results were secured. However, hydroxyethyl cellulose has the advantage not possessed by methyl cellulose that the viscosity of a given solution thereof may be decreased if desired by heating to 90-100 C. so as to facilitate the treatment of the paper.

The substitution of pyruvic aldehyde for glyoxal in the modification of the process exemplified yields products somewhat less suitable for use as toweling, the acetal derivative of pyruvic aldehyde being more easily hydrolyzed by water and somewhat volatile at the drying temperature for the paper.

If desired, the glycerine may be omitted from the solution described in the example. In that case, however, the finalproduct or dry sheet containing the acetal is distinctly less'flexible and pliable than that produced with the solution described in the example.

There may be substituted in 'the impregnating composition, for the water-soluble cellulose ethers, the corresponding ethers of other carbohydrates such as water-soluble hydroxyalkyl starches, although the resultant products are inferior in strength and flexibility to those made from cellulose ethers.

Thus, glyoxal may be designated a ketoacetaldehyde; and pyruvic aldehyde may be designated a ketopropionaldehyde. Such aldehydes as have not more than five carbon atoms in the molecule are preferred.

I claim:

1. As a new article of manufacture, absorbent 1 paper of high wet strength and resistant to linting, said paper containing as a size the product of the reaction between a water-soluble ether derivative of a higher polyose and a water-solu-- ble aldehyde having the structure designated by the formula I II wherein R represents either hydrogen or an alkyl group.

2. As a new article of manufacture, absorbent paper of high wet strength and resistant to linting, said paper containing as a size the waterresistant reaction product of a water-soluble cellulose ether with a water-soluble a ketoaldehyde of the paraflin series having not more than three Paper towels, napkins, absorbent tissues and V the like made by the present process have decided advantages over ordinary paper towels in having a high resistance to linting, a higher wet strength, and in being highly absorbent, particularly where the amount of the condensation product present in the towel does not greatly exceed 1.5% of the dry weight of the untreated paper toweling.

The term water-soluble cellulose ether and similar expressions appearing in the claims are intended to include those water-soluble partially alkylated and aralkylated celluloses produced, respectively, by treating a suitable cellulosic material with an alkylating agent such as dimethyl sulfate or methyl chloride; or with an aralkylating agent such as benzyl chloride; and those water-soluble hydroxyalkyl celluloses produced by treating such a cellulosic material with an hydroxyalkylating agent such as ethylene oxide, propylene oxide or ethylene chlorhydrin.

The aldehydes utilized in the present invention may also be designated as water-soluble or water miscible cc ketoaldehydes of the paraffin series.

structure designated carbon atoms in the molecule.

3. A felted structure comprising fibers in felted formation, said structure being impregnated with a product formed by concurrently condensing a water-soluble cellulose ether and a polyhydric alcohol with a water-soluble aldehyde having the by the formula wherein R represents either hydrogen or an alkyl group. r

4. A felted structure comprising fibers in felted formation, said structure being impregnated with a co-acetal of a water-soluble cellulose ether and a polyhydric alcohol with a water-soluble a ketoaldehyde of the paraflin series having not more than three carbon atoms in the molecule.

5. As a new article of manufacture, absorbent paper of high .wet and dry strengths, having a high resistance to linting during service, said paper containing as a size a product formed by the conjoint condensation of a water-soluble cellulose ether, a polyhydric alcohol and glyoxal.

6. As a new article of manufacture, absorbent paper of high wet and dry strengths, having a high resistance to linting during service, said paper containing as a size a product formed by the conjoint condensation of a water-soluble cellulose ether, a polyhydric alcohol and pyruvic aldehyde.

7. A preformed moisture absorbent felted sheet of high wet strength, said sheet being formed of organic fibrous material having at least some of the fibers thereof coated with a material produced by the concurrent condensation of a water-soluble cellulose ether and a polyhydric alcohol with a water-soluble a ketoaldehyde of the parafiin series having not more than three carbon atoms in the molecule.

8. A preformed moisture absorbent felted sheet of high wet strength, said sheet being formed of organic fibrous material having at least some of the fibers thereof coated with a material produced by the concurrent condensation of a water-soluble cellulose ether and a polyhydric alcohol with glyoxal.

9. A preformed moisture absorbent felted sheet of high wet strength, said sheet being formed of soluble cellulose ether and a polyhydric alcohol with pyruvic aldehyde.

10. A web of fibrous organic material having moisture absorbent properties, high wet and dry strengths and resistance to tear when wet, said web having at least some of the fibers forming it coated with a co-acetal of a water-soluble cellulose ether and a polyhydric alcohol with a water-soluble aldehyde having the structure designated by the formula wherein R represents either hydrogen or an alkyl group.

11- As a new article of manufacture, fibrous I sheet material especially adapted for the manufacture of absorbent paper toweling, comprising a base of fibrous organic material impregnated .with the product formed by the conjoint condensation of a water-soluble cellulose ether, a

hyde of the paraffin series, said aldehyde containing not more than three carbon atoms in the molecule, and thereafter removing the elements of water from the thus treated fibrous material, thereby depositing upon the fibers a product of the conjoint condensation of said water-soluble ether, polyhydric alcohol, and aldehyde.

15. In the process of producing an absorbent paper sheet having high dry and wet strengths and which is resistant to linting, the steps which comprise applying to fibrous cellulosic material polyhydric alcohol and a water-soluble a keton-o-o-n wherein R represents either hydrogen or an alkyl group, and thereafter heating the thus treated sheet, thereby depositing within the felted sheet an acetal derivative of said cellulose ether with said aldehyde.

13. The process of producing an absorbent paper sheet having high dry and wet strengths and which is resistant to linting, which process comprises applying to a preformed felted sheet of organic fibrous material of relatively low wet strength an aqueous solution containing a watersoluble cellulose ether, a polyhydric alcohol, and a water-soluble aldehyde having the structure designated by the formula wherein R represents either hydrogen or an alkyl group, and thereafter heating the thus treated sheet to remove the elements of water therefrom, thereby depositing upon the fibers of said felted sheet a product of the conjoint condensation of said water-soluble ether, polyhydric alcohol, and aldehyde.

14. Process of producing an absorbent paper sheet having high dry and wet strengths and which is resistant to linting, which process comprise applying to organic fibrous material of relatively low wet strength an aqueous solution containing a water-soluble cellulose ether, a polyhydric alcohol, and a water-soluble a ketoaldean aqueous solution containing a water-soluble cellulose ether, a polyhydric alcohol, and a water-soluble aldehyde having the structure designated by the formula a. O I R-o-g-n wherein R represents either hydrogen or an alkyl group, and thereafter heating the thus treated fibrous material to remove the elements of water therefrom, thereby depositing upon the fibers a product of the conjoint condensation of said watier-soluble ethenlpolyhydric alcohol, and aldeyde. I

16. A felted structure comprising fibers in felted formation, said structure being impregnated with a product formed by concurrently condensing a water-soluble hydroxyalkyl cellulose and a polyhydric alcohol with a water-soluble aldehydle having the structure designated by the formu a a l R t t H wherein R represents either hydrogen or an alkyl group.

1'1. As a new article of manufacture, absorbent paper of high wet and dry strengths, having a high resistance to linting during service, said paper containing as a size a product formed by the conjoint condensation of a water-soluble hydroxyalkyl cellulose, a polyhydric alcohol and'a water soluble a ketoaldehyde of the paraflin series having not more than three carbon atoms in the molecule.

18. A preformed moisture absorbent felted sheet of high wet strength, said sheet being formed of organic fibrous material having at least some of the fibers thereof coated with a material produced by the concurrent condensation of a water-soluble hydroxyalkyl cellulose and a polyhydric alcohol with a water-soluble a ketoaldehyde of the paraffin series having not more than three carbon atoms in themolecule.

19. Process of producing an absorbent .paper sheet having high dry and wet strengths and which is resistant to linting, which comprises applying to organic fibrous material of relatively low wet strength, an aqueous solution containing a water-soluble hydroxyalkyl cellulose, a polyhydric alcohol, and a Water-soluble a ketoaldehyde of the paraflin series containing not more than three carbon atoms in the molecule, and thereafter removing the elements of water from the thus treated fibrous material, thereby depositing upon the fibers a product of the conjoint condensation of said water-soluble hydroxyalkyl cellulose, polyhydric alcohol and aldehyde.

AUBREY E. BRODERICK. 

